1. Field of the Invention
This invention relates to a novel process for the preparation of 1-aminoanthraquinone using as starting material 5-nitro-1,4,4a,9a-tetrahydroanthraquinone (hereinafter referred to simply as 5-nitrotetrahydroanthraquinone) expressed by the formula: ##SPC1##
2. Description of the Prior Art
1-Aminoanthraquinone is important as an intermediate for anthraquinone-base disperse dyes, vat dyes and pigments, and has been heretofore synthesized through anthraquinone-1-sulfonic acid obtained by the sulfonation of anthraquinone. However, this prior art process is difficult to practice since it involves the use of a mercury catalyst in the sulfonation step, thus presenting many problems concerning the work environment and environmental pollution. Various methods for the preparation of 1-aminoanthraquinone as alternatives to the above process have been investigated, among which a method of preparation using nitration and reduction reactions of anthraquinone has been assumed to be most effective. However, this method using the nitration and reduction of anthraquinone involves the use of large amounts of sulfuric acid and nitric acid, offering problems in handling of the acids and in treatment of the resultant waste liquor. Additionally, 1-aminoanthraquinone obtained by this method contains a large quantity of by-products including diamino compounds and the 2-amino compound, and must essentially be purified by complicated operations for use as an intermediate of dye. Thus, this method is not successful from the industrial point of view.
There have also been proposed several process for the preparation of 1-nitroanthraquinone wherein 5-nitro-1,4-naphthoquinone (hereinafter referred to simply as 5-nitronaphthoquinone) is condensed with 1,3-butadiene to give 5-nitrotetrahydroanthraquinone, followed by oxidation to obtain 1-nitroanthraquinone. For example, according to N. N. Woroshtzov et al. (Khim. Nauka i Prom, 5, 474 - 475, 1960), 1-nitroanthraquinone can be obtained by condensing 5-nitronaphthoquinone and 1,3-butadiene in ethanol and oxidizing the resultant condensation product with air in an alcoholic alkali solution. Moreover, French Pat. No. 1,486,803 (Institut Premyslu Organiznco) describes a process for the preparation of 1-nitroanthraquinone by reacting butadiene with 5-nitronaphthoquinone in nitrobenzene and oxidizing the resultant reaction product by means of nitrobenzene in the presence or absence of piperidine without isolation of the reaction product. 1-Nitroanthraquinone obtained by these processes can be readily converted into 1-aminoanthraquinone by an ordinary reduction method. However, these processes have a vital disadvantage in that when 5-nitrotetrahydroanthraquinone which is obtained by condensation of 5-nitronaphthoquinone and 1,3-butadiene is dissolved in a suitable solvent after isolation thereof, or as it is without isolation, and then air is fed into the solution for oxidation in the presence of a base such as piperidine, various by-products are also produced, so that 1-aminoanthraquinone obtained by reduction of the resultant 1-nitronaphthoquinone with the various by-products is low in purity. As a result, it is difficult to use such 1-aminoanthraquinone as an intermediate for dyes.